It is common for an organisation to wish to securely and quickly save data, for example transactional data, or changes to data made during a period. A backup data copy is created in case the primary data file is damaged in some way or is lost. In many organisations this is done by copying a database/data records to tape in a separate, often overnight, data backup operation, typically whilst users are not altering the data. It is also common to have backup data records deliberately stored at a different geographical site than that at which the primary data file is stored. For example, backup tapes may be taken home with senior information technology (I.T.) staff, or a backup data record may be made over a wide area network (WAN) to keep it in a different physical location.
For some organisations there is a difficulty in reliably backing up their overnight data. If the volume of data to be backed up is large (and sometimes it could be 50 GB or more) it might take something of the order of 4 hours or so to back it up onto tape. Some organisations may have a long working day: for example from 6.00 a.m. to 10.00 p.m. This leaves only 8 hours to perform the backup. This is usually long enough. However, if there is a problem backing up the data the backup can run out of time to complete the backup operation before organisation wishes to start changing the original data again. For example, if a tape drive performs two hours of a backup operation and then starts to get repeated data error signals it may cancel that backup and start again. If this happens again (and possibly again) then no backup may have been completed by the time that the organisation opens for business the next morning. This leaves the I.T. manager with a choice: deny personnel access to their computers (or at least those functions that will alter the data being backed up until the backup is complete), or allow the “live” data to be modified without there being a backup of the previous day's data/changes to the data.
The first option is hardly ever attractive. The second option is also not attractive, but is often the only practical possibility.
Possible solutions to this problem include manning the backup facility overnight so as to have human intervention/input to problems (most overnight backups are performed with no humans present to oversee them), but this is not popular with the people involved.
Another possibility is to make the backup operation faster so that more re-tries are possible in any given period.
There is a common drive in service provider computer environments to architect the I.T. infrastructure to avoid having a single point of failure. Current tape library arrangements, for example in the backup scenario described, are not fault tolerant. The tape drive is often a single point of failure. If there is a problem with the tape drive then the whole data storage tape library fails. It is known to avoid this by using RAIT technology (Redundant Array of Inexpensive Tapes). However, the “inexpensive” part of RAIT is a misnomer: having multiple tape drives, each with their own array of tapes and an automatic tape changer, is very expensive. Furthermore, if a backup is distributed over several tapes there is then a need to keep a set of tapes together: to associate them in some way. This also is inconvenient for the person taking out of the building the backup tapes since they now have a bundle of tapes.
Tape is the preferred medium for storing backup data because it is cheap, robust, and can be removed from the tape drive and re-inserted many times. Tape cassettes can withstand the treatment given to them (e.g. put in a bag or case, thrown in the car, driven around/shook up, left in warm/cold environments) and still be inserted/removed from a tape drive very many times before the insertion/removal operation, or simply their use once inserted, wears them out. They can also store a lot of data.
Floppy discs can be inserted/removed from a disc drive, but they are less robust, and may not withstand the insertion/reinsertion so many times, and currently cannot store so much data.
Whilst removable hard discs exist, they are very expensive and are less robust, and are not designed for regular, repeated, insertion/removal every day for a year, or years.
Furthermore, if a tape physically breaks it is often possible to read data at regions of the tape away from the break. If a disc physically breaks that is far from easy to do (if it is possible at all). Thus tapes also have a greater chance of being able to have data recovered from them in the event of a physical accident to the data carrier.
A number of prior art arrangements of data protection are known, see for example JP 1100102262, where data stored in a hard disc at a main host computer is stored on an off-site tape library. JP 580144270 discusses another data storage device. WO 90/06580 deals with a tape drive and a disc drive mounted in the same housing having common control circuitry. Also, U.S. Pat. No. 5,822,184 shows a tape and disc drive being mounted in the same housing.
U.S. Pat. Nos. 6,161,169 and 5,805,921 disclose bus/buffer management algorithms and techniques.